Process and apparatus for interbed injection in plate reactor arrangement

ABSTRACT

A process and apparatus for indirectly exchanging heat with narrow channel in a heat exchange type reaction zone uses manifold space to interconnect the common ends of channels and to provide controlled distribution of additional reactants. The invention simplifies the operation and construction of the heat exchanging type reaction zone by directly communicating reaction channels and/or heating channels with a manifold located at the end of the channels. The manifold can provides the extra function of mixing additional reactants. The invention promotes simplified intermediate injection of reactants over tube and shell heat transfer arrangements that have been used for similar purposes. Improved process control has particular benefits for exothermic reactions. The narrow channels are preferably defined by corrugated plates. The reaction channels will contain a catalyst for the promotion of the primary reaction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of application Ser. No. 09/149,841filed Sep. 8, 1998, now U.S. Pat. No. 6,168,765, the contents of whichare hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to plate type exchanger arrangementsfor containing a reaction zone and indirectly heating the reaction zonewith a heat exchange fluid.

BACKGROUND OF THE INVENTION

In many industries, like the petrochemical and chemical industries,contact of reaction fluids with a catalyst in a reactor under suitabletemperature and pressure conditions effects a reaction between thecomponents of one or more reactants in the fluids. Most of thesereactions generate or absorb heat to various extents and are, therefore,exothermic or endothermic. The heating or chilling effects associatedwith exothermic or endothermic reactions can positively or negativelyaffect the operation of the reaction zone. The negative effects caninclude among other things: poor product production, deactivation of thecatalyst, production of unwanted by-products and, in extreme cases,damage to the reaction vessel and associated piping. More typically, theundesired effects associated with temperature changes will reduce theselectivity or yield of products from the reaction zone.

Exothermic reaction processes encompass a wide variety of feedstocks andproducts. Moderately exothermic processes include methanol synthesis,ammonia synthesis, and the conversion of methanol to olefins. Phthalicanhydride manufacture by naphthalene or orthoxylene oxidation,acrylonitrile production from propane or propylene, acrylic acidsynthesis from acrolein, conversion of n-butane to maleic anhydride, theproduction of acetic acid by methanol carbonylation, and methanolconversion to formaldehyde—represents another class of generally highlyexothermic reactions. Oxidation reactions in particular are usuallyhighly exothermic. The exothermic nature of these reactions has led tomany systems for these reactions incorporating cooling equipment intotheir design. Those skilled in the art routinely overcome the exothermicheat production with quench or heat exchange arrangements. Extensiveteachings detail methods of indirectly exchanging heat between thereaction zone and a cooling medium. Indirect heat exchange refers to thetransfer of heat from one fluid to another fluid across a common surfacewithout intermixing of the fluids as normally occurs in quench systems.The art currently relies heavily on tube arrangements to contain thereactions and supply indirect contact with the cooling medium. Thegeometry of tubular reactors poses layout constraints that require largereactors and vast tube surfaces to achieve high heat transferefficiencies.

Other process applications accomplish indirect heat exchange with thinplates that define channels. The channels alternately retain catalystand reactants in one set of channels and a heat transfer fluid inadjacent channels for indirectly heating or cooling the reactants andcatalysts. Heat exchange plates in these indirect heat exchange reactorscan be flat or curved and may have surface variations such ascorrugations to increase heat transfer between the heat transfer fluidsand the reactants and catalysts. Many hydrocarbon conversion processeswill operate more advantageously by maintaining a temperature profilethat differs from that created by the heat of reaction. In manyreactions, the most beneficial temperature profile will be obtained bymaintaining substantially isothermal conditions. In some cases, atemperature profile directionally opposite to the temperature changesassociated with the heat of reaction will provide the most beneficialconditions. For such reasons, it is generally known to contact reactantswith a heat exchange medium in cross flow, co-current flow, or countercurrent flow arrangements. A specific arrangement for heat transfer andreactant channels that offers more complete temperature control can befound in U.S. Pat. No. 5,525,311, the contents of which are herebyincorporated by reference. Other useful plate arrangements for indirectheat transfer are disclosed in U.S. Pat. Nos. 5,130,106 and 5,405,586.

Isolating reactants from coolants at the inlets and outlets of plateexchanger arrangements leads to elaborate designs and intricatemanufacturing procedures. Simplification of the fluid transfer at theinlets and outlets of plate exchanger improves the cost effectivenessand practicality of plate exchanger usage in many processes. Improvedarrangements for injecting reactants at intermediate locations along theprocess flow path can also improve reactor performance in terms ofselectivity and yields.

It is, therefore, an object of this invention to simplify a plateexchanger design for the indirect heat transfer and injection ofreactants in reaction zone.

It is a further object of this invention to simplify the feed andrecovery of reactants and heat exchange fluid from a heat exchangereactor that uses a channel arrangement.

BRIEF SUMMARY OF THE INVENTION

In broadest terms, this invention incorporates intermediate injection ofprocess fluids into open chamber portions that circulate fluid from aplurality of heat exchange channels to another plurality of heatexchange channels to control process reaction conditions and reactantconcentrations. A chamber communicates the heated channels and thereaction zone across common ends of the narrow channels whilesimultaneously mixing reactants the ends of the channels to providesimple transfer of fluids between different sets of channels. Thechamber permits additional temperature control by the addition orremoval of reactants, cooling fluids or other streams at an intermediatepoint in the complete channel flow paths. Insertion of additionalchambers along the flow path of either the reaction or heated channelsprovides locations for more temperature adjustment and control.

Suitable channel arrangements may exchange heat directly across a commonheat exchange surface or may use an intermediate heat transfer fluid toindirectly transfer heat from a cooling or heating zone to the reactionzone. In this manner the intermediate heat transfer fluid allowsoptimization of conditions for endothermic and exothermic reactions indifferent channels while simultaneously providing temperature adjustmentcontrol for differences in heat generation from the exothermic reactionand heat absorption from the endothermic reaction. For example, onearrangement of the intermediate heat transfer fluid may place thecooling zone and the reaction zone at different portions of commonchannel and may pass the intermediate fluid through adjacent channels totransfer heat out of reaction channels at one location and transfer heatback into the heated channels at a downstream channel location. In otherarrangements, the intermediate channels and the reaction channels maylie in a parallel arrangement between the heated channels to adjust thetemperature in the reaction channels through the heated channels.

Variation of the catalyst loading within the reaction channels and theaddition of catalyst for endothermic reactions may satisfy differentprocessing objectives. For example, short loading of catalyst inreaction channels can provide a space above or below the reaction zonefor additional feed preheat or effluent cooling. Again, extending theheated channels can provide additional surface area for open channelheat exchange against the exiting reaction zone effluent or the incomingreactants.

Although usefull in any heat producing reaction or heat absorbingreaction, this invention finds its greatest benefit in exothermicreactions. As an example, process and reactor arrangements in accordancewith this invention may be especially usefull for producing ethyleneoxide. A particularly beneficial process application for this inventionis in the production of phthalic anhydride (PA) by the oxidation oforthoxylene. The reaction apparatus feeds the orthoxylene feed to adistribution manifold that injects a controlled amount of orthoxylene inadmixture with the air or other oxygen containing gas. Injection of theorthoxylene into the manifold prevents the presence of the orthoxyleneand oxygen in explosive proportions. The manifold preferably contains apacking making, such as inert particles, to reduce the volume of thechamber and minimize the amount of mixed orthoxylene and oxygen. Theplate arrangement of the heat exchange reactor quickly dissipates thehigh heat of reaction associated with the synthesis of the PA. Theenhanced temperature control improves product selectivity while alsopermitting increased throughput.

The reaction apparatus designed in accordance with this invention offersa high degree of flexibility in temperature control with a relativelysimple plate reactor arrangement. The outer containment vessel cancompletely support the plate arrangement from either its top or bottomsDirect passage of heated reactants from the heated channels outlets toreaction channels inlets through a common chamber eliminates the needfor manifolding and its associated welding at at least one end of thetypically thin channel plates.

The presence of narrow heat exchange channels for cooling the reactionzone and heating the reactants constitutes an essential requirement ofthis invention. With respect to fluid flow through the reaction channelsand heated channels, fluid may have co-current flow or cross flow withrespect to some of the channels. The plates defining the channels forcontaining the reactions and heat exchange gases may have anyconfiguration that produces narrow channels. A preferred form of thebeat exchange elements is relatively flat plates having corrugationsdefied therein. The corrugations serve to maintain spacing between theplates while also supporting the plates to provide a well supportedsystem of narrow channels. Additional details on the arrangement of suchplates systems are shown in U.S. Pat. No. 5,525,311, the contents ofwhich are hereby incorporated by reference.

One distinct advantage discovered with the plate heat exchanger designof this invention permits an increase in the overall feed rate ofoxidated reactants without increasing their overall concentration infeed stream mixtures that comprise air or oxygen. Notably for productionof PA, the process and plate reactor arrangement of this inventionsignificantly increases the amount of orthoxylene that can enter thereaction zone for a given constant air feed rate to the reactionchannels.

Suitable plate arrangements may also incorporate perforated plates. Mostadvantageously, perforated plates allow the controlled quantities of theheated reactant to flow directly into the reaction channels. Perforatedplates disperse the introduction of the reactant over a desired portionof the reaction zone. Those skilled in the art will recognize othervariations in plate configurations that can provide additional benefitsto the integrated reaction stages.

Accordingly, in a broad process embodiment, this invention contactsreactants with a catalyst in a reaction zone while indirectly heating orcooling the reactants in the reaction zone by indirect heat exchangewith a heat exchange fluid. The process passes a reactant-containingstream through a first plurality of channels defined by spaced apartplates and recovers a first channel effluent. A first channel effluentstream collects in a manifold volume having direct communication withoutlets of the first plurality of channels. The process injects anintermediate fluid into the manifold volume and mixes at least a portionof the first channel effluent to produce a second channel input stream.The second channel input stream passes from the manifold volume directlyinto the inlets of a second plurality of channels defined by spacedapart plates. The process recovers a second channel effluent stream fromthe outlets of the second portion of spaced apart plates. At least thereactant stream or the second channel input stream contacts a catalystin the first plurality of channels or the second plurality of channels.The process indirectly exchanges heat between the reactant-containingstream, the second channel input stream, and a heat exchange fluidpassing through channels defined by the spaced apart plates.

In a more specific process embodiment, this invention is a process foroxidizing reactants with a catalyst in a reaction zone while indirectlycooling the reactants in the reaction zone by indirect heat exchangewith a heat exchange fluid. A first inlet stream containing oxygen andan oxidation reactant passes through a first plurality of channelsdefined by spaced apart plates and into contact with an oxidationpromoting catalyst. An effluent from the outlets of the first pluralityof channels passes directly into a manifold volume containing a packingmaterial. The process injects additional oxidation reactant into themanifold volume and mixes fluids therein to produce a second inletstream containing oxygen and an oxidation reactant. The second inletstream passes from the manifold volume directly to the inlets of asecond plurality of channels defined by the spaced apart plates andthrough an oxidation promoting catalyst contained in the secondplurality of channels. The process recovers a second channel effluentstream from the outlets of the second portion of spaced apart plates andindirectly exchanges heat with the first and second plurality ofchannels by passing a heat exchange fluid through the heat exchangechannels defined by the spaced apart plates. In a preferred form of theexothermic process, the first inlet stream comprises air andorthoxylene; the intermediate stream comprises orthoxylene; and thefirst and second plurality of channels contain an orthoxylene oxidationcatalyst that promotes the production of the second channel effluentcomprising phthalic anhydride.

A specific apparatus embodiment of this invention is a particular platereactor design that advantageously uses the chamber design of thisinvention to independently pass at least two different fluids throughtwo adjacent sets of channels in counter-current flow. The specificreactor arrangement may use a perforated manifold arrangement to enhancethe even distribution of entering reactants.

In a more complete apparatus embodiment, this invention is a reactionarrangement for contacting reactants with a catalyst in a reaction zonewhile indirectly heating or cooling the reactants in the reaction zoneby indirect heat exchange with a heat exchange fluid. The apparatuscomprises a plurality of spaced apart plates that define a firstplurality of reaction channels and a second plurality of reactionchannels for retaining a catalyst material in at least one of the firstand second plurality of channels. The first plurality of reactionchannels defines a first plurality of reaction inlets and a firstplurality of reaction outlets. The second plurality of reaction channelsdefines a second plurality of reaction inlets and a second plurality ofreaction outlets. The apparatus includes a distribution manifolddefining a manifold volume in direct communication with the fistplurality of reaction outlets and with the second plurality of reactioninlets and containing an injector for injecting a fluid into themanifold volume. In a more limited form of this apparatus embodiment theplurality of plates defines heat exchange channels between the first andsecond plurality of reaction channels and the heat exchange channelsdefine heat exchange inlets for receiving a heat exchange fluid and heatexchange outlets for discharging a heat exchange fluid. A particularlybeneficial arrangement of manifolds uses a first distribution headerthat partially covers one side of a stack of heat exchange platesdefined by the plurality of plates. The first distribution headerextends across at least one of the heat exchange inlets or heat exchangeoutlets to define a first distribution space that communicates directlywith the inlet or outlet across which it extends to distribute orcollect the heat exchange fluid. A second distribution header partiallycovers the one side of the stack of heat exchange plates and partiallycovers at least a portion of the first distribution header. The seconddistribution header extends across at least one of the first reactioninlets or the first reaction outlets to define a second distributionspace that communicates directly with the inlet or outlet across whichit extends to distribute or collect fluid.

Additional embodiments, arrangements, and details of this invention aredisclosed in the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three dimensional view schematically showing a plate reactorarranged in accordance with this invention.

FIG. 2 is a schematic drawing of a flat plate element showing acorrugation pattern.

FIG. 3 is an isometric view of corrugated plates forming flow channels.

FIG. 4 is a three dimensional view of a plate reactor arrangement and acontainment vessel arranged in accordance with this invention.

FIG. 5 is a section of FIG. 4 taken at lines 5—5.

FIGS. 6 and 7 are sections of FIG. 5 taken at line 6—6 and 7—7,respectively.

FIG. 8 is a three-dimensional view of a plate channel arrangement anddistribution header arrangement similar to that shown in FIG. 4.

FIG. 9 is a section of FIG. 8 taken along lines 9—9.

FIGS. 10 and 11 are graphs showing the temperature profile andconversion parameters along the path length of tubes in a tubulararrangement for PA production by orthoxylene oxidation.

FIGS. 12-17 are graphs showing the temperature profile and conversionparameters along the path length of channels in plate heat exchangereactor arrangements for producing PA by orthoxylene oxidation.

DETAILED DESCRIPTION OF THE INVENTION

This invention may be useful in any endothermic or exothermic processwhere a reactant or a portion of a reactant provides a heat sink forheating an endothermic reaction or for cooling an exothermic reaction inan arrangement of plate exchanger elements. Additional requirements ofthis process for compatibility with a plate exchanger arrangement willtypically require that there be a relatively low ΔT between any heatexchange zone and reaction zone. Differential temperatures of 200° C. orless are preferred for this invention. Differential pressures willremain low and will typically reflect pressure drop requirements throughthe catalyst bed. Ordinarily the differential pressure across plateelements will not exceed 0.5 MPa.

The reaction channels will contain a catalyst for promoting thereaction. Suitable catalysts for the previously mentioned processes aswell as other process applications are well known to those skilled inthe art. Catalyst in a particulate form may fill the reaction channelsto the degree desired for reaction time and pre-reaction heating orpost-reaction cooling in the reaction channels. As an alternate to aparticulate catalyst, the catalyst may also be coated on the surface ofthe plates in the various reforming zones. It may be particularlyadvantageous to coat the reaction catalyst onto the plates to provide anupper catalytic section and a lower catalyst-free section that ismaintained in heat relationship across the channel defining plates witha secondary catalytic zone.

The heat exchange fluid used in the process or apparatus of thisinvention may be any type of fluid that can provide the necessarycooling or heating capacity. A wide variety of heat exchange fluids maysatisfy the requirement for heating or cooling. Such fluids will includeintegral process streams as well as auxiliary fluids. The fluid mayabsorb or release heat by sensible, latent or reactive means. For highlyexothermic processes, molten salts or metals may be particularly usefulas a heat exchange medium.

Where suitable for balancing heat requirements of a particular reaction,those skilled in the art are aware of particular catalysts for promotingcomplimentary exothermic and endothermic reactions. Such catalysts mayadvantageously reside in the heating channels to provide reactivecooling as well as cooling from the sensible or latent heat of thereactants. Examples of such an endothermic and exothermic catalystcombinations are in steam reforming and in the oxidative heating of anethylbenzene dehydrogenation reaction by combustion of the hydrogenproduced therein. Such arrangements are particularly suited forincorporation into a multiple pass channel arrangement thatinterconnects only two pairs of adjacent channels and places anexothermic reaction channel between an alternate heating channel andendothermic reaction channels. In a configuration providing such a threepass arrangement the relatively cold reactants flow into the heatingchannels where indirect heat exchange with the reaction channelsprovides the respective beating and cooling. Flowing the reacted streamfrom the exothermic reaction channels into the endothermic reactionchannels provides additional cooling to the reaction channels across theshared of plates that define the endothermic reaction channel as well asthe adjacent exothermic reaction channels.

FIG. 1 illustrates a basic flow arrangement for the process of thisinvention. The discussion of FIG. 1 uses the production of phthalicanhydride (PA) as an example of a specific context for an exothermicprocess; however the general principles apply to any exothermic processincluding those previously enumerated. Looking then at FIG. 1 for abasic flow arrangement of this invention, a relatively cold feed streamcomprising orthoxylene and air in a proportion of about 70 g oforthoxylene per Nm³ of air enters the process and undergoes heatexchange in a conventional heat exchanger (not shown). Typically thefeed stream exchanges heat with a PA gas product stream carried from anozzle 12 of a heat exchange reactor 10. The preheated feed streampasses via an inlet nozzle 13 to a distribution chamber 14. Heatexchange reactor 10 contains a plurality of heat exchange plates 11 thatdefine sets of channels. Distribution chamber 14 supplies the heatedfeed to a first set of reaction channels 15 having inlets in chamber 14.Reaction channels 15 contain an oxidation catalyst through which thefeed passes.

As the entering feed passes through the reaction channels 15, a coolingfluid passes through a plurality of beat exchange channels 16 in a flowdirection shown by arrows 17 which establishes a cross flow relationshipto the flow in channels 15. Suitable containment chambers (removed forclarity) on the top and bottom of reactor 10 distribute and collect theheat exchange fluid. Plates or other closures seal the tops and bottomsof reaction channels 15 to prevent the heat exchange fluid from enteringthe channels. The large surface area provided by the plates 11 providerapid cooling of the reactants and good temperature control.

A manifold volume 18 collects the heated reactant stream from the firstset of channels. Top plate 19 covers manifold space 18. The broken awayportion of plate 19 shows the relative flow direction of the reactantsout of channels 15 in a direction of arrow 20. A pipe lance 21 havingperforations 22 injects additional orthoxylene into manifold volume 18.The injected orthoxylene mixes with the partially reacted stream fromchannels 15 to produce a feed stream with additional orthoxylene forfurther reaction in a second plurality of reaction channels 23. Platesor other closures seal the sides of the heat exchange channels 16 toprevent the reactants exchange fluid from entering the heat exchangechannels. Manifold volume 18 will ordinarily contain a packing materialto minimize the potential volume for explosive mixtures of theoxygen-containing gas and orthoxylene. While the drawing only shows onepipe lance, multiple pipe lances may be used to promote enhanced mixingof the partially reacted stream and the additional orthoxylene inmanifold volume 18. Pipe lances 21 may be place immediately adjacent tothe inlets 24 of the reaction channels 23. Arrows 25 show the flowdirection of the reactants that enter channels 23.

As the second reaction mixture enters channels 23 it contacts additionalcatalyst contained therein. The resulting reaction releases more heatthat is removed by the passage of the cooling fluid through channels 16.A collection chamber 26 collects PA products and reactants from channels23 for removal by nozzle 12 and subsequent heat exchange, as previouslydescribed.

Reaction channels 15 and 23 contain catalyst material that promotes theoxidation of the orthoxylene. Suitable catalyst materials are well knownto those skilled two in the art. The catalyst material may reside in thechannels as a coating applied to plates or as discrete particles. Theinlets and outlets of channels 15 and 23 are open to fluid flow. Wherethe catalyst material comprises a particulate material, a screenmaterial located across the inlets and outlet prevents catalyst fromescaping out of the reaction channels.

Distribution chamber 14, manifold volume 18, or collection chamber 26may contain extra fluid withdrawal or addition pipes. Further fluidaddition or withdrawal may provide a number of supplementary functions.For example, addition and return of fluid may provide cooling by passinga portion of the withdrawn reactant-containing steam through a coolerand recirculating the cooled fluid to reaction channels.

It is also not necessary to the practice of this invention that eachreaction channel be alternated with a heat exchange channel. Possibleconfigurations of the reaction section may place two or more heatexchange channels between each reaction channel to reduce the pressuredrop on the heat exchange medium side. The double channel arrangementmay be defined by a plate separating adjacent heat exchange channelsthat contain perforations. The use of packing or perforated plates canenhance heat transfer with the reaction channels while providing goodcirculation over the entire cross-section of the heated channel.

In general, the invention relies on relatively narrow channels toprovide the efficient heat exchange across the thin plates. In general,the channel width should be less than one inch on average with anaverage width of less than ½ inch preferred. Suitable plates for thisinvention will comprise any plates that allow a high heat transfer rate.Thin plates are preferred and usually have a thickness of from 1 to 2mm. The plates are typically composed of ferrous or nonferrous alloyssuch as stainless steel. Preferred alloys for the plates will withstandextreme temperatures and contain high proportions of nickel and chrome.The plates may be formed into curves or other configurations, but flatplates are generally preferred for stacking purposes. Again, each platemay be smooth and additional elements such as spacers of punched tabsmay provide fluid turbulence in the channels.

Preferably, each plate has corrugations that are inclined to the flow ofreactants and heat exchange fluid. The corrugations maintain a variedchannel width defined by the height of the corrugations. In the case ofcorrugations, the average channel width is most practically defined asthe volume of the channels per the cross-sectional area parallel to theprimary plane of the plates. By this definition corrugated plates withessentially straight sloping side walls will have an average width thatequals half of the maximum width across the channels.

FIG. 2 shows the preferred corrugation arrangement for plates 11 thatdivide the central portion of heat exchange reactor 14 into heatexchange channels and reaction channels. The corrugation pattern canserve at least two functions. One function is to structurally supportadjacent plates. The other function is to promote turbulence forenhancing heat exchange efficiency in the narrow reaction channel. FIG.2 shows corrugations defined by ridges 27 and valleys 28. The frequencyor pitch of the corrugations may be varied as desired to promote anyvarying degree of turbulence. Therefore, more shallow corrugations withrespect to the fluid flow direction, as shown by ridges 27 and valleys28, will produce less turbulence whereas a greater corrugation pitchwith respect to the direction of fluid flow, as shown by ridges 29 andvalleys 30, provide increased turbulence where desired. The pitch of thecorrugations and the frequency may also be varied over a single heatexchange channel to vary the heat transfer factor in different portionsof the channel. Preferably, the channels may contain a flat portion 31about their periphery to facilitate closure of the channels about thesides and tops where desired.

FIG. 3 shows a typical cross-section of a corrugated plate arrangementwherein the corrugations of plates 32 extend in an opposite direction tothe corrugations of plates 33 thereby defining alternate reactionchannels 34 and heated channels 35. FIG. 3 illustrates the preferredarrangement of corrugated plates where the herring bone pattern on thefaces of opposing corrugated plates extends in opposite directions andthe opposing plate faces contact each other to form the flow channelsand provide structural support to the plate sections.

Additional channels defined by the plates can provide a variety ofsupplementary functions. In addition to channels for the beatingreactants and/or cooling the reaction zone while containing theexothermic reaction. other channel functions may provide additionalpreheating of the feed for the exothermic reaction zone, cooling of theeffluent from the exothermic reaction zone, and retaining of a catalystfor an endothermic reaction.

A reactor arrangement 36 specially suited for providing gooddistribution of reactant and heating medium with a co-current orcounter-current flow of the reactant and heat exchange fluid is shown inFIGS. 4-7. In this reactor arrangement, a cylindrical vessel 37surrounds a plurality of heat exchange plates. A top plate 42 covers thevessel 37. A broken away section of top plate 42 shows the plurality ofheat exchange plates 38 that define a plurality of heat exchangechannels 39, a first plurality of reaction channels 40, and a secondplurality of reaction channels 41.

Considering again PA production as a non-limiting example for explainingthe apparatus of FIGS. 4-7, an oxidation gas enters the reactor 36through an inlet nozzle 43 that communicates with an outer distributionchamber 44. Outer distribution chamber 44 distributes the incomingoxidation gas over the surface of a curved screen 45. Curved screen 45defines an inner distribution chamber 46. Orthoxylene enters innerdistribution chamber 46 via a pipe distributor 47 through a row ofperforations that extend over the length of inner chamber 46. As theoxidation gas enters inner chamber 46, injection of the orthoxylenemixes the reactants to provide a PA feed mixture. The mixture ofreactants enters the inlets of the first set of reaction channels 40.Inner chamber 46 may again contain a particulate material to fill thevoid volume of chamber 46 and reduce the potential for damage fromexplosive reaction mixtures. A divider plate 48 separates the volume ofthe outer distribution chamber 44 and inner distribution chamber 46 froman outer collection chamber 49 and an inner collection chamber 50.

The PA feed mixture passes into the first set of reaction channels 40.Reaction channels 40 contain a catalyst for the promotion of PAproduction by orthoxylene oxidation. A reacted mixture containingprimarily PA and unreacted oxidation gas exits reaction channels 40 andenters an outlet chamber 51. A sidewall 52 forms a lateral boundary ofoutlet chamber 51 and an intermediate inlet chamber 53. Intermediateinlet chamber 53 may again contain particulate material to reduce anyvoid volume, to reduce the potential for any accumulation of anexplosive mixture. Lateral sidewall 52 may provide an impervious surfaceso that the effluent from reaction channels 40 transfers directly fromand remains in outlet chamber 51.

Alternately, lateral sidewall 52 may provide a perforated surface suchas the screen surface 45 so that the effluent from reaction channels 40may enter a supplementary chamber 54 that transfers at least a portionof the effluent from the reaction channels 40 to the intermediate inletchamber 53. If desired, a partition plate 55 may block any direct fluidtransfer from outlet chamber 51 into intermediate inlet chamber 53thereby directing all fluid flow through the supplementary chamber 54.Directing all of the fluid flow through supplementary chamber 54 andacross a perforated wall of lateral sidewall 52 can improve distributionof the oxidation gas and PA over intermediate inlet chamber 53.

Regardless of the fluid flow path between chambers 51 and 53, anadditional injection pipe 56 having perforations 57 will mix additionalorthoxylene with the oxidation gas and PA for distribution into thesecond set of reaction channels 41. Additional oxidation of theorthoxylene to produce additional PA takes place by contact with anorthoxylene oxidation catalyst in the second set of reaction channels41. Inner collection chamber 50 collects any unreacted oxidation gas andorthoxylene as well as the PA product. Outer collection chamber 49receives the mix of reactants and PA that exits the reactor 36 through anozzle 87.

Throughout the oxidation reaction, a cooling fluid circulates in heatexchange channels 39 to control the temperature of the oxidationreaction. The cooling fluid enters the side of cylindrical vessel 37through a cooling inlet nozzle 58. Nozzle 58 delivers the cooling fluidto a cooling distribution chamber 59. Coolant partition plates 60 and 61segregate the incoming fluid from the chambers that contain thereactants or products. A plurality of distribution sub-channels 62 opensto distribution chamber 59 along plate 61 to receive cooling fluid anddistribute it to heat exchange channels 39. A plurality of collectionsub-channels 63 at the opposite end of heat exchange channels 39collects the warmed coolant and transfers it via openings 67 into acoolant collection chamber 64. The collected coolant exits chamber 64through a nozzle 69, typically for cooling and return to inlet 58. Apair of partition plates 65 and 66 segregates the collected coolant fromthe reactant-containing chambers. Openings 67 are spaced along thelength of partition 66. As more clearly shown in FIG. 6, sub-channels 62and 63 have a semicircular shape. An open cordal face of sub-channel 63faces chamber 64 and defines opening 67 for communicating the warmcoolant into chamber 64. As shown in FIG. 5, a closure plate 68 coversthe opposite end of collection sub-channel 63 to prevent coolant fromentering outer chamber 49. Distribution subchannels 62 have a similaropen cordal face 70 that receives coolant from nozzle 58 via chamber 59.

The segregation and distribution of fluid across the open channels areprovided by blocking reaction channels that are in communication withsub-channels 62 and by blocking the openings to those portions of theheat exchange channels that are in communication with inner collectionchamber 50, outlet chamber 51, inner distribution chamber 46, andintermediate inlet chamber 53. FIG. 7 more clearly shows thisdistribution pattern where open inlets to the first set of reactionchannels are indicated by 40′. Open inlets to the second set of reactionchannels are indicated by 41′ and open inlets to the heat exchangechannels are indicated by 39′. The solid squares indicate where theopenings to the heat exchange and reaction channels are closed to fluidflow.

The reactor design shown in FIGS. 4-7 circulates the reactants in all ofthe channels 40 in the same direction and co-currently to the flow inthe adjacent heat exchange channels 39 while it circulates all of theflow in the reaction channels 41 in the opposite direction to the flowin the reaction channel 40 and counter-currently to flow in heatexchange channels 39. Simple changes to the channel distribution andcollection arrangements of the reactor facilitates easy variation in therelative flows and flow direction through the channels. In a furtherexample of one such variation, FIG. 8 shows a modified form of thechannels and collection and distribution spaces of FIGS. 4-7. Thearrangement of FIG. 8 passes a heat exchange fluid through a perforatedface 71 of a distribution chamber 72 in the direction indicated byarrows 73. Distribution chamber 72 directs the incoming cooling fluid toinlets 74 of heat exchange channels 75. The cooling fluid flows out ofheat exchange channels 75 and into a collection chamber 76 formed inpart from a perforated wall of profile wire 77. As the cooling fluidflows out of distribution chamber 72, it passes around inletsub-channels 78 and outlet sub-channels 79. As the cooling fluid flowsinto collection chamber 76, it flows around redistribution sub-channels80.

Reactants enter and leave reaction channels through inlet sub-channel 78and outlet subchannel 79, respectively. Again in the case of PAproduction, a mixture of orthoxylene and oxygen enters the inletsub-channel 78 in the direction shown by arrows 81. Sub-channels 78distribute the incoming reactants to a first set of reaction channels 82for flow towards the redistribution sub-channels 80. Redistributionsub-channels 80 receive unreacted reactants, primarily oxidationcomponents and the PA product. Injection pipes 83 inject additionalorthoxylene reactants into the sub-channels 80 for mixing with theeffluent from the first set of channels 82. Sub-channels 80 mix andredistribute the orthoxylene oxidation components and PA products to asecond set of reaction channels 84. Particulate material or other spacedisplacing means may be located in sub-channels 80 to prevent thefilling of the sub-channel volume with explosive fluid mixtures. Aftercontact with additional catalyst in the second set of reaction channels,the PA product and any unreacted components flow into collectionsub-channels 79 for recovery from the chamber and plate reactionapparatus.

Top 85 of the channel arrangement is partially broken away in FIG. 8 toshow the relative direction of fluid flow through the various channels.The flow through the reaction channels is all in the same direction andthe flow through the reaction channels alternates direction from channelto channel. FIG. 9 shows the pattern of channel openings and blockagesassociated with distribution chamber 72 in order to provide thedirection of fluid flow through the appropriate channels. The inlets forthe first set of reaction channels that receive reactants fromsub-channel 78 are indicated by 82′. Reference numeral 74 indicates thelocation for the open inlets to the heating channels that are locatedbetween the distribution and collection sub-channels. Reference numeral84′ shows the location of the outlets that deliver reactants andproducts from the second set of reaction channels into the sub-channels79. The other solid squares indicate where the openings to the heatexchange and reaction channels are closed to fluid flow.

EXAMPLES

To more fully illustrate the process and apparatus of this invention andits advantages, the following examples present the calculated operationof a tubular heat exchange type reactor and the calculated operation ofdifferent plate channel reactor arrangements of the type depicted in theFIGURES. All of the examples use the reactor arrangements for theoxidation of orthoxylene to phthalic anhydride. The numerical model useswell established kinetic data and experimentally developed heat transferdata. All of the catalytic data was based on performance parameters fora silicon carbide base material surface coated vanadium pentoxide havinga surface area of 2000 cm²/g. All examples operated to keep thephthalide content in the effluent at less than 1000 ppm in the PAproduct. All of the examples modeled the use of molten salt as thecooling medium. Comparison of the numerical model against publishedliterature for similar modeling studies verified the accuracy of thenumerical model.

Example 1

The example established the performance of the tubular reactor base caseand produced similar results to current industrial tubular reactorperformance. In this base case, a feedstock of air containing anorthoxylene concentration of 75 g/Nm³ feed passes through a three meterlong tube having a diameter of 25 mm at a mass flux rate of 10,000kg/m²/hr which produces a 0.3 bar pressure drop along the tube. Thetubular reactor model uses a ring or shaped particle having a diameterof 9 mm. Circulation of a salt bath at a temperature of 698° K aroundthe shell side of the tubes provides cooling. The feed enters thetubular reactor at a temperature of about 700° K. The final phthalidecontent in the PA product was below 1000 ppm. FIG. 10 graphicallydepicts the temperature profile over the length of a representativetube. The tube achieves a peak temperature of about 835° K within thefirst 50 cm of its path length. FIG. 11 illustrates an essentiallycomplete conversion of orthoxylene with about the first 100 cm of tubelength. As also presented by FIG. 11, continued conversion in the tubesreduces the concentration of orthotolualdehyde and phthalide to levelsof less than 1000 ppm while raising the PA conversion to about 83%.

Example 2

The basic plate heat exchanger type reactor operates at the sameorthoxylene inlet concentration and mass flux through the heat exchangechannels as the tubular reactor. The channel arrangement contains a 2 mmspherical catalyst in a 6 mm gap between channels. To maintain the same0.3 bar pressure drop across the channels as across the tubes, theprocess flux in the plate reactor arrangement drops to 7500 kg/m²/hr.Nevertheless, the sizing of the plate exchange reactor maintains thesame ratio of heat transfer surface area to catalyst surface area on aper reactor volume basis as in the tubular reactor arrangement. At thesame 75 g/Nm³ concentration of orthoxylene in the air feed, the processinlet temperature in the plate exchanger reactor increases 15° C. abovethe tubular reactor case or to a temperature of about 713° K to maintainthe same phthalide level in the PA product. Even with an increased inlettemperature, FIG. 12 shows the peak temperature in the channelsdecreasing to about 815° C., representing about a 20° C. temperaturedrop relative to the tubular reactor case. Again, FIG. 13 shows a rapidconversion of orthoxylene along the path length of the plate exchangereactor with about the same conversion to PA and orthotolualdehydephthalide to levels below 1000 ppm. Thus, the temperature reduction ofthis example demonstrates that the plate heat exchange reactor has abouta 30% overall greater heat transfer ability than the tubular reactor.

Example 3

Example 3 evaluates increases in the concentration of the orthoxylene inthe air to the plate exchange reactor over the range of from 75 g/Nm³ to110 g/Nm³ to determine the concentration that produces the same peaktemperature in the plate heat exchange reactor as in the tubularreactor. Heat from the additional orthoxylene oxidation requiresincreasing the circulating salt temperature from the 713° K in Examnple2 to about 717° K to keep the phthalide concentration below 1000 ppm inthe PA product. At a concentration level of about 105 g/Nm³, the peaktemperature of the plate reactor (see FIG. 14) approaches the samemaximum temperatures as the tubular reactor arrangement. As establishedby FIG. 15, the maximum orthoxylene concentration can increasesignificantly over the tubular case reactor by use of the plateexchanger while still maintaining the PA conversion of about 83 mol-%.

Example 4

Example 4 demonstrates the effect on temperature and conversion ofstaging the injection of orthoxylene at an intermediate point in thechannels to reestablish a maximum concentration of 75 g/Nm³. Thisexample decreases initial injection of feed to reduce the process fluxat the inlet of the plate reactor to 5525 kg/m²/hr for the first stageof orthoxylene injection. The arrangement injects additional orthoxyleneat 30 cm along the path length of the heat exchange reactor. With thelower process flux, the temperature of the circulating salt bath dropsto 700° K, the equivalent of the tubular reactor inlet temperature. Thepath length of the channels in this example increases to a total of 130cm. That provides an additional 30 cm for the fist stage whilemaintaining the same 100 cm of second stage that was used in Examples 2and 3. The additional length decreases the phthalide content below 1000ppm in the PA product. Nevertheless, even with the increased length,total pressure drop remains below the 0.3 bar value of the tubularreactor example. FIG. 16 displays a maximum peak temperature of below810° K in the first stage. FIG. 17 shows an essentially completeorthoxylene conversion within the first 30 cm of the injection point.FIG. 17 demonstrates continued PA conversion at over 83 %. As a result,a process unit using the tubular type to produce 50 kMta of PA wouldrequire 33 cubic meters of catalyst. By comparison, a plate beatexchange reactor using multiple feed injection to produce the sameamount of PA product requires only about 12.8 m³ of catalyst and therebysignificantly reduces capital costs of the plate reactor arrangementrelative to the tubular reactor arrangement. Consequently, this exampleshows an effective doubling of orthoxylene feed concentration withstaged feed injection over that of the tubular reactor.

Overall the examples establish numerous process advantages of the platereactor arrangement over the tubular reactor arrangement. A comparisonof the examples shows the overall added heat efficiency of using a plateheat exchange reactor arrangement that introduces a mixture of air andorthoxylene at a single inlet point for the production of phthalicanhydride. Using the plate reactor arrangement with an increasingorthoxylene concentration in the air at the single feed inlet producesadditional advantages. Moreover, multiple feed ejection of theorthoxylene in the plate reactor arrangement substantially reduces theplate reactor arrangement costs. Such savings can include a 50 %reduction in air compression costs and substantial reduction in capitalcosts due to a smaller relative size for plate reactor versus thetubular reactor.

What is claimed is:
 1. A process for contacting reactants with acatalyst in a reaction zone while indirectly heating or cooling thereactants in the reaction zone by indirect heat exchange with a heatexchange fluid, the process comprising: a) passing a reactant-containingstream through a first plurality of channels defined by a stack ofplates and recovering a first channel effluent; b) collecting the firstchannel effluent stream in a manifold volume having direct communicationwith outlets defined by the plates that define the first plurality ofchannels; c) injecting an intermediate fluid directly into the manifoldvolume and mixing at least a portion of the first channel effluent toproduce a second channel input stream; d) passing the second channelinput stream from the manifold volume directly into inlets of a secondplurality of channels defined by said stack of plates and having directcommunication with the manifold volume; e) recovering a second channeleffluent stream from outlets of the second plurality of channels; f)contacting at least one of the reactant stream and the second channelinput stream with a catalyst in the first plurality of channels or thesecond plurality of channels; and g) indirectly exchanging heat with aheat exchange fluid and at least one of the reactant-containing streamsand the second channel input stream, wherein the heat exchange fluidpasses through channels defined by said stack of plates.
 2. The processof claim 1 wherein the reactant-containing stream exchanges heat withthe second channel input stream across common plates.
 3. The process ofclaim 1 wherein the stack of plates define heat exchange channelsbetween the first and second plurality of channels.
 4. The process ofclaim 3 wherein a heat exchange fluid passes through the heat exchangechannels in relative cross flow to the reactant-containing stream in thefirst plurality of channels and to the second channel input stream inthe second plurality of channels.
 5. The process of claim 1 wherein thesecond plurality of channels contains a catalyst for promoting anendothermic or exothermic reaction.
 6. The process of claim 1 wherein atleast one of the first or second plurality of channels contains acatalyst for promoting an exothermic reaction and the manifold volumecontains a packing material.
 7. A process for oxidizing reactants with acatalyst in a reaction zone while indirectly cooling the reactants inthe reaction zone by indirect heat exchange with a heat exchange fluid,the process comprising: a) passing a first inlet stream containingoxygen and an oxidation reactant through a first plurality of channelsdefined by a stack of plates and into contact with an oxidationpromoting catalyst; b) passing an effluent from outlets defined by theplates that define the first plurality of channels directly into amanifold volume containing a packing material; c) injecting additionaloxidation reactant into the manifold volume and mixing fluids therein toproduce a second inlet stream containing oxygen and an oxidationreactant; d) passing the second inlet stream from the manifold volumedirectly to inlets of a second plurality of channels defined by saidstack of plates and through an oxidation promoting catalyst contained inthe second plurality of channels; e) recovering a second channeleffluent stream from the outlets of the second plurality of channels;and f) directly exchanging heat with the first and second plurality ofchannels by passing a heat exchange fluid through heat exchange channelsdefined by said stack of plates.
 8. The process of claim 1 whereindifferent sides of common plates define heat exchange channels betweenindividual channels in the first plurality of channels and secondplurality of channels.
 9. The process of claim 7 wherein the heatexchange fluid passes through the heat exchange channels in relativecross flow to the fluid in the first and second plurality of channels.10. The process of claim 7 wherein the first inlet steam comprises airand orthoxylene; the intermediate stream comprises orthoxylene; and thecatalyst in the first and second plurality of channels comprises asilicon carbide base material surface coated with vanadium pentoxide;and the second channel effluent comprises phthalic anhydride.
 11. Theprocess of claim 7 wherein the heat exchange fluid passes through afirst distribution header that distributes the heat exchange fluiddirectly to inlets of the heat exchange channels defined by the stack ofplates and the first inlet stream passes through a packing material in asecond distribution header that distributes the first inlet streamdirectly to inlets defined by the plates that define the first pluralityof channels and that surrounds at least a portion of the firstdistribution header.
 12. The process of claim 11 wherein a permeablewall of the second distribution header admits an oxygen-containing fluidinto the second distribution header and an injector injects theoxidation reactant directly into the interior of the second distributionheader.
 13. The process of claim 12 wherein the oxygen-containing fluidcomprises air; the oxidation reactant comprises orthoxylene; and thesecond channel effluent comprises phthalic anhydride.
 14. A reactionapparatus for contacting reactants with a catalyst in a reaction zonewhile indirectly heating or cooling the reactants in the reaction zoneby indirect heat exchange with a heat exchange fluid, the apparatuscomprising: a) a stack of plates defining a first plurality of reactionchannels and a second plurality of reaction channels for retaining acatalyst material in at least one of the first and second plurality ofchannels and defining heat exchange channels; b) a first plurality ofreaction inlets and a first plurality of reaction outlets defined by thefirst plurality of reaction channels; c) a second plurality of reactioninlets and a second plurality of reaction outlets defined by the secondplurality of reaction channels; d) a distribution manifold defining amanifold volume in direct communication with the first plurality ofreaction outlets and the second plurality of reaction inlets; e) anaddition fluid injector extending into the manifold for injecting afluid into the manifold volume; and f) heat exchange inlets forreceiving a heat exchange fluid and heat exchange outlets fordischarging a heat exchange fluid defined by the heat exchange channels.15. The apparatus of claim 14 wherein the plurality of plates arearranged in a stack having a side upon which at least one of heatexchange inlets or outlets are defined and upon which at least one ofthe reaction inlets or reaction outlets are defined, a firstdistribution header partially covers said side and extends across atleast one of the heat exchange inlets or heat exchange outlets to definea first distribution space that communicates directly with the heatexchange inlets or outlets across which it extends to distribute orcollect the heat exchange fluid and a second distribution headerpartially covers said side and partially covers at least a portion ofthe first distribution header and extends across at least one of thefirst reaction inlets or the first reaction outlets to define a seconddistribution space that communicates directly with the first reactioninlets or outlets across which it extends to distribute or collectfluid.
 16. The apparatus of claim 15 wherein a containment vesselsurrounds the stack and the second distribution header defines a fluidpermeable sure to distribute or collect fluid from the containmentvessel across the surface of the second distribution header.
 17. Theapparatus of claim 16 wherein the second distribution space distributesa reaction fluid to the first reaction inlets and an inlet fluidinjector extends into the second distribution space to introduce aninlet fluid directly into the second distribution space.
 18. Theapparatus of claim 14 wherein the reaction channels have an averagewidth of less than 1 inch.
 19. The apparatus of claim 18 wherein theplates are flat.
 20. The apparatus of claim 19 wherein the plates definecorrugation and the corrugations maintain spacing between the plates.